Does the timing of my sale within my corporation's fiscal year affect how much tax I pay?

Yes, timing can genuinely affect your tax outcome, in more than one way. If you're selling shares personally, the calendar year your sale closes in determines which tax year the gain lands in, which affects what other income or gains it stacks on top of and can push you into a higher tax bracket in that particular year depending on timing. If instead the transaction is a share sale that gives the buyer control of the corporation, that acquisition of control triggers a deemed year-end immediately before the change in control, under specific Income Tax Act rules — this shortens the corporation's taxation year at that point, affects how things like available deductions and loss carryforwards are calculated for that shortened year, and can affect instalment obligations.

Timing near a corporation's normal year-end can also affect how much passive investment income has accumulated in a given year, which in turn can interact with rules affecting the small business deduction and other tax attributes, separate from the sale itself.

Because these effects depend on your specific numbers, existing losses, and corporate structure, working through actual timing scenarios with an accountant before setting a closing date can make a real difference to your after-tax result.